maxima and L. pallida is the Bladder Kelp (Macrocystis pyrifera also
known as Blaaskelp and Blaas
Seebamboes), the least common of
the cold-water West Coast kelps.
This kelp was previous called M.
angustifolia in South Africa, but
molecular research has shown that
globally only one species of Macrocystis exists. The species is relatively
delicate, vine-like, and bears numerous blades at regular intervals
along its slender stipe. At the
plant’s apex, the new blades are
fused, gradually separating as they
grow. The blades possess numerous
marginal spines and a single gasfilled bladder at their bases, which
allows this kelp to remain afloat
and erect in the water column. In
addition, the blades are rippled, a
feature that is important for increasing absorption of nutrients in
relatively low flow environments
cha racteristic of sheltered lagoons
and bays. Unlike the previous two
species of kelp, an individual holdfast in this species can bear multiple stipes. Large populations of M.
pyrifera are only found at two locations near Cape Town; one at Kommetjie, the other at Robben Island.
Related to Ecklonia maxima is a
much smaller species of kelp known
as the Spiny Kelp ( Ecklonia radiata
also known as Stekelrige Kelp and
Stekelrige Seebamboes). This spe-
cies is restricted to the warm temperate to subtropical shores of the
south and southern east coasts. The
species is notably stunted, reaching
an average length of only about 1
m although plants in excess of 2 m
have been recorded in deep subtidal areas throughout the South
Coast, and shallow subtidal areas
along the Eastern Cape coast that
are
influenced
by
localised
upwelling. Unlike E. maxima, this
species has a comparatively small
holdfast and short solid stipe that
lacks a gas-filled bulb. In adult
plants, the primary blade is generally short and gives rise to densely
crowded secondary blades that may
be smooth or variably rippled. Secondary blades in this species are
characteristically spiny, alluding to
the species’ common name.
Similarities between kelp ‘forests’
and terrestrial forests
Despite their one obvious difference (terrestrial vs marine), terrestrial forests and kelp communities
share a number of features. Both
ecosystems are considered nutrientadvantaged systems. In terrestrial
forest ecosystems, nutrients are
replenished from leaf litterfall and
the accumulation of humus in the
soil. In kelp forest ecosystems, nutrients are kept in constant supply
due to wind-induced mixing of wa-
A clump of juvenile kelp plants showing their typical
root-like holdfasts, stem-like stipes and blades formed
at the distal ends of the stipes.
ter layers and through upwelling.
Both
ecosystems
are
threedimensional (stratified) comprising
canopy, sub-canopy or understorey,
and ground-dwelling organisms.
The dominant canopy-forming organisms (trees and kelp plants) utilize most, if not all, of the available
sunlight and make efficient use of
their nutrient-rich surroundings
through their monopoly of the light
regime and their efficient uptake of
the plentiful available nutrients. The
canopy-forming trees and kelp
plants are relatively fast-growing
organisms that are highly productive, attaining many meters in
height (length). Canopy and Dissolved Organic Matter (COM/DOM
i.e. leaf/blade litter), respectively
the main food source, are derived
directly from the canopy-forming
organisms, and form the base of
most of the food webs in these
ecosystems. Solar and Wind energy
drives the productivity cycles and
the availability of nutrients in both
ecosystems. With so much similarity
between these ecosystems, surely
we cannot be wrong by referring to
the marine counterparts as Kelp
Forests?
Original Source
Maneveldt G.W. 2011. Kelp Forests:
Forests of a different kind. Veld &
Flora 97(4): 168-170.
At St. James and Kalk Bay along the Cape Peninsula,
kelp can be seen for several metres offshore and several hundred metres alongshore.